Solid-state color imaging devices and methods for making them are well known in the art. For example, Hartman, U.S. Pat. No. 4,315,978; Martin, U.S. Pat. No. 4,335,087 and Pace and Blood, U.S. Pat. No. 4,764,670 disclose such devices having high resolution and methods for making them wherein color filter arrays formed from dyeable photopatternable coatings are fabricated on light-sensing semiconductor substrates. A color filter array is the lithographically patterned set of colors which can be placed on top of an electronic imager enabling it to sense colors. Color filter array coatings typically comprise dyeable photopatternable coatings, intermediate barrier layers, and non-dyeable photopatternable coatings, for example, those used for planarizing layers and protective overlayers.
A particularly useful process for preparing a solid-state color image sensing device having color filter arrays includes the steps of applying a coating of a dyeable photopatternable material to the surface of a silicon-containing wafer substrate having an array of charge-handling semiconductive photosensors and bonding pad areas, imagewise exposing and developing the coating so as to form a pattern corresponding to a filter element, and dyeing the exposed and developed pattern by contacting the pattern with a solution comprising a dye. Subsequently, the steps of coating, imagewise exposing, developing, and dyeing the remaining filter element are repeated, differing only in the pattern and/or its location and the dye employed, to form sets of color filters, for example, sets containing red, green and blue or cyan, magenta and yellow filter elements or combinations thereof. To achieve high resolution, the color filter elements must be in microregistration with the underlying array of photosensors. This means that the filter elements and the photosensor array must be precisely aligned on a micron scale.
Each of the numerous steps involved in the fabrication process affects the quality, for example, the resolution and/or chrominance discrimination, of the ultimate solid-state color image sensing device. In view of the exacting criticalities involved, the yield of acceptable high quality, high resolution solid-state color image sensing devices tends to be less than 100% through the fabrication process. In view of the costs associated with the substrates upon which color filter arrays are fabricated in making solid-state color image sensing devices, it would be highly desirable to be able to recover substrates from partly or fully fabricated devices so that the substrate could subsequently be used to produce another solid-state color image sensing device.
Thus, the problem facing the art has been to provide a process for stripping color filter array coatings from a substrate of a solid-state color image sensing device so that the substrate can be used to produce another solid-state color image sensing device, which effectively removes all of the coating in a reasonable amount of time, even when the coating has been baked and hardened by various processing steps, and which does not adversely affect the electrical properties of the device, the exposed bond pads or the backside of the water.
A wide variety of stripping approaches have been investigated. However, none of these has been fully satisfactory for one or more of the above-noted reasons. For example, color filter array coatings have been contacted with boiling nitric acid and hot triethanolamine. Such chemical stripping treatments do not efficiently remove all of the photopatternable coating from the substrate, even after extended periods of contact time. Coatings have also been subjected to etching by oxygen plasma, however, etching processes tend to be very time-consuming and, in many cases, leave a residue remaining on the substrate surface.